There has been much attention directed recently on the need to conserve natural resources by reducing needless consumption of energy. One of the major uses of energy is environmental temperature sustaining means, in particular, heating and cooling systems which, as a result, are one of the prime targets for energy conservation. Various automated temperature control systems have been developed in attempts to reduce the energy consumption of an environmental heating and cooling system of a space particularly when the space is unoccupied.
One such system is a programmable thermostat wherein the user programs the thermostat in accordance with the expected occupancy status of the space. Thus, for example, in a home heating and cooling system where the homeowner does not expect to be home between the hours of 9:00 a.m. and 5:00 p.m., the thermostat may be programmed to reduce the heating or cooling requirements during those hours. Similarly, in the late night hours when the occupants of the house would be sleeping, the system is also programmed to reduce the heating or cooling requirements during those hours. Thus, the system is programmed to operate at full heating and cooling capacity only during the expected hours of occupation, namely, in the morning between rising and leaving the house and in the evening between arriving home and going to bed. There are, however, drawbacks associated with such systems, one major drawback being that if the space is occupied during the hours from 9:00 a.m. to 5:00 p.m., then it is necessary to override the programming of the programmable thermostat. Additionally, should there be minor variations from the routine on particular days, then it is generally not possible to allow for such variations in the programming of the thermostat. The result is either that the temperature of the space once occupied does not reach the comfort level desired until the heating or cooling system is automatically activated and brings the temperature to the comfort level desired, or, that the heating or cooling system is automatically activated before the space is occupied thereby needlessly wasting energy.
Control systems have also been described wherein the environmental heating and controlling system is set to a first setpoint for when the room is occupied and to a second, more energy efficient setpoint when the room is unoccupied. Sensors are provided to determine when the room is occupied and thereby adjust the heating and cooling system setpoint. However, such systems suffer from the drawback that it will take some time from the initial indication of occupancy of the space until the heating and cooling system can bring the temperature of the space up to the comfort level desired when the space is occupied.
There thus remains a need for a simple but efficient temperature control system which can easily be used and adapted to varying occupancy status of a space.